The Spanish rider, who joined from Movistar, broke his femur in a crash on the snow this week.
He has undergone an operation, which was said to be a success, but will face an estimated three months on the sidelines.
Prades was a key signing for the French team amid a winter of change. They have lost sponsors Nippo and Provence, as well as a number of riders, to the EF Education team. Furthermore, Cyclingnews exposed a series of allegations relating to missed salary payments and bullying behaviour, which the team have denied.
Prades, 33, rode for Caja Rural and Euskadi-Murias before hitting the WorldTour with Movistar in 2019 following his wins at the Tour of Turkey and Tour of Norway. He has won the Vuelta Aragón and a stage of the Tour de la Provence for the team but was not offered a contract renewal for 2021.
His season was disrupted first by the pandemic and then by the Tour de Pologne crash on his return, which left him with a fractured vertebra.
With few options at WorldTour level, he decided to sign for Team Delko, who operate in the second-division ProTeam ranks.
"He really has that competitive spirit and he has more a profile of a leader in a ProTeam than a good helper in the WorldTour," said team manager Philippe Lannes.
However, the team will now be without a rider who they envisaged bringing a number of wins to the table. Prades had been set to race Paris-Nice in March but will not appear until April at the earliest.